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Warning: Do not look directly at the Sun with the naked eye or any unfiltered optical instruments
It's possible to see the amazingly dynamic nature of our nearest star in white light and hydrogen alpha; Pete Lawrence tells us how
Sunspot groups, or active regions, take on a whole new appearance in hydrogen alpha. Dark sunspots become harder to see, partially hidden under the surrounding chromospheric blanket. Around them, dark fibrils follow the intense magnetic fields associated with these regions. Large, bright areas called plage appear throughout and around sunspot groups.
The edge of the Sun's disc seems to have a thin skin running around it. This is a cross-section of the chromosphere. Under good seeing you can make out that it's made up of tiny jets known as spicules. Together, they make the edge of the Sun appear 'furry'.
Prominences and Filaments
Giant clouds of magnetically influenced hydrogen plasma can often be seen hanging off the edge of the Sun through a hydrogen-alpha filter. Known as prominences, these can change appearance day-to-day or, in extreme circumstances, real time. When seen against the chromosphere away from the limb, they appear dark and are known as filaments.
Active regions may also show dynamic bright regions. Tiny star-like points of light called Ellerman Bombs may come and go, each releasing the same energy as several million atomic bombs. Larger ribbons of light called flares are associated with magnetic reconnection events, which may throw out huge clouds of charged particles known as coronal mass ejections.
A hydrogen-alpha filter shows the Sun's inner layer of atmosphere, known as the chromosphere, which sits on top of the photosphere. This is covered in a coarse, magnetically influenced light and dark pattern collectively known as dark mottling. The pattern is visible across the entire disc and makes the Sun resemble a giant orange.
Sunspots appear dark against the photosphere, often occurring in groups known as active regions. A typical sunspot shows a dark inner core called the umbra, and a lighter surrounding region called the penumbra. Sunspots appear dark because they are cooler than the surrounding photosphere.
The limb-darkened edge of the Sun's disc provides excellent contrast for viewing faculae. These are magnetically affected regions where the Sun's 'surface' becomes more transparent, allowing you to see into the deeper, hotter areas below.
When the Sun's disc is viewed through a white light filter, the centre appears brighter than the edge. This is called limb darkening and occurs because at the centre of the disc you can see deeper into hotter, brighter layers.
The Sun's visible surface, or photosphere, is covered in a fine pattern called solar granulation. This can be tricky to see and image as it's easily hidden by poor seeing. Granulation represents the tops of huge rising convective cells reaching the photosphere.
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Solar projection is suitable for small refractors. The idea is to point the scope at the Sun and place a screen, typically a piece of white card, behind the telescope's eyepiece. This method can show solar granulation, dark sunspots and bright faculae.
White Light Solar Filter
An inexpensive sheet of white light solar safety material can easily be fashioned into a filter for use with any type or size of amateur telescope. It allows you to view and image granulation, sunspot groups and faculae.
An entry level hydrogen-alpha scope such as the Coronado PST is able to show prominences, dark mottles, filaments and many of the bright phenomena associated with active regions such as plage and flares.
H-Alpha Scopes and Filters
For finer detail, larger aperture, narrower bandwidth hydrogen-alpha scopes are available, typically for several thousand to tens of thousands of pounds. Solar hydrogen-alpha filter kits in a similar price range can also be used to convert night-time telescopes.
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